What is an inactivated vaccine?

Inactivated vaccines are made from viruses or bacteria that have been rendered noninfectious, often by heat or chemicals. Because the pathogen cannot multiply, these vaccines are generally very safe and are used for diseases such as polio in its injectable form and hepatitis A. They often need booster doses because they may not create as strong or long-lasting an immune response as live attenuated vaccines. Inactivated vaccines have been a major part of routine immunization for decades. They are a key example of how vaccines can protect without using live organisms.